Many of commercially practical polymer electrolyte fuel cells are a stack of a plurality of cell units each of which includes a cell sandwiched by a pair of plates in which gas-flow channels are formed, where the cell is composed of an anode, a cathode, and a polymer electrolyte membrane, the polymer electrolyte membrane being disposed between the anode and cathode. The polymer electrolyte fuel cell, when operated, generates electricity through electro-chemical reaction while the cathode-side channels are supplied with air as oxidizer and the anode-side channels are supplied with a fuel gas.
Meanwhile, a problem of such polymer electrolyte fuel cells is that the polymer electrolyte membrane needs to be moistened during operation to maintain the ionic conductivity of the membrane. To solve this problem, in many conventional methods, humidified air or humidified fuel gases are supplied to the fuel cells. Japanese Laid-Open Patent Application No. 5-41230 discloses another method in which the fuel gas and water are each supplied through dedicated channels out of a plurality of anode-side channels so that supplying of the fuel gas to the anode and moistening of the polymer electrolyte membrane are both effectively performed and the fuel cell can be cooled.
To secure an excellent cell performance in fuel cells, the fuel gas should be extended to every corner of the anode. For this purpose, care should be taken in this type of polymer electrolyte fuel cells so that the anode-side channels are not blocked with water since it may block the fuel gas flow.
In consideration of this problem, conventional methods allow the fuel gas and water to flow downwards through the channels directed vertically and discharge the fuel gas and water to outside the fuel cell through a common discharge pipe displaced at the lower part of the fuel cell. However, such methods still have a problem that the fuel gas is blocked when meniscuses of water are formed due to capillary phenomenon at the downstream edge of the anode-side channels where three phases (fuel gas exhaust as gas phase, the channel plate as solid phase, and water as liquid phase) gather together.
FIG. 1 shows the problem that the fuel gas is blocked when meniscuses are formed at the downstream edge of the anode-side channels. When such meniscuses are formed, the channels are blocked and the fuel gas is unequally supplied to the anode.
Such channel blockage may be prevented if the channels are widened to prevent the occurrence of the capillary phenomenon. However, widening the channels is not preferable since it increases the electrical resistence in the fuel cell.
For the same purpose, the fuel gas may be supplied at high pressure so that the gas passes through the channels at high speed. In this case, however, an apparatus for supplying the fuel gas at high pressure and collecting it is required. Such a construction is not preferable for achieving compact systems, such as portable ones.
To gain excellent cell performance from polymer electrolyte fuel cells, the polymer electrolyte membrane needs moistening in entirety.
However, this type of conventional polymer electrolyte fuel cells have a problem that different amounts of water run through a plurality of channels. That is to say, among a plurality of anode-side channels, more water is supplied to the channels near upstream of the water distribution path. Accordingly, a part of the polymer electrolyte membrane facing the channels near downstream of the water distribution path is less moistened.
It is possible to solve this problem by increasing the amount of water supply to extend water to every corner of the polymer electrolyte membrane. In this case, however, a pump with a large capacity is required. Moreover, the fuel gas supply effeciency decreases since water is excessively supplied to a part of the channels.
It is therefore an object of the present invention to provide a polymer electrolyte fuel cell in which fuel gas and water are supplied to anode-side channels to generate electric power, where the fuel gas is stably supplied to the anode in entirety and the polymer electrolyte fuel membrane can be moistened in entirety.